1. Field of the Invention
The present invention relates to a radio communication apparatus and a radio communication method. As an example of the radio communication apparatus, a radio base station and a mobile station used in the mobile radio communication system introducing the W-CDMA (UMTS) communication system are considered. As an example of the radio communication method, a radio communication method used in this system may be thought.
2. Description of the Related Art
Data transmission between the radio communication apparatuses is conducted via the radio links. When a plurality of radio communication apparatuses (transmitting stations) are provided for data transmission and one radio communication apparatus (receiving apparatus) is provided for receiving the data from these transmission stations via a shared channel, the transmission timing must be controlled for these transmitting stations.
Such transmission timing control will be briefly explained with reference to FIG. 1.
FIG. 1 is a diagram for explaining the data transmitting method among the radio communication apparatuses, illustrating an example of transmission of packet data.
The radio communication apparatus A corresponds to a receiving station, while the radio communication apparatuses B and C, to the transmitting stations.
In the transmission method, a transmitting station B having the data (assumed as 120 Bytes for three packets) desired to be transmitted to the receiving station A transmits first a transmission reservation request (control packet data) to the receiving station A. This transmission reservation request includes the packet number information (assumed as 3) desired to be transmitted from the transmitting station B.
Upon reception of the transmission reservation request from the transmitting station B, the receiving station A evaluates acknowledgment or non-acknowledgment of acceptance of the reservation. When the other transmitting stations do not desire to make a transmission, the receiving station A accepts this transmission reservation request and transmits the reservation acknowledgment to the transmitting station B. This reservation acknowledgment includes a delay information (in this case, delay is not generated and therefore N=0) instructing to delay transmission timing of the packet data by N packets timing and a packet number information indicating the number of packets acknowledged for transmission.
Accordingly, upon reception of the reservation acknowledgment, the transmitting station B waits for the timing for transmission of N packets in accordance with the delay information (in this case, the nearest packet transmission timing) and transmits the packet data (40 Bytes) in this timing to the receiving station A.
The packet data is received with the receiving station A. Here, the receiving station A judges acknowledgment or non-acknowledgment of reception using error detection bits included in the receiving packet data. When reception is normally completed, the receiving station A transmits the ACK signal to the transmitting station B. The receiving station A transmits, when the packet data is not received normally, the NACK signal to the transmitting station B, urging the transmitting station B to retransmit the packet data.
Here, the transmitting station B transmits, because it receives the ACK signal, respective packet data (40 Bytes) to the receiving station A in the next packet transmission timing, and in the second next packet transmission timing.
As explained above, the transmitting data in total of 120 Bytes are transmitted to the receiving station A.
On the other hand, the transmitting station C also issues a transmission reservation request (for two packets) as illustrated in the figure to the receiving station A and receives the reservation acknowledgment from the receiving station A.
However, at the time of transmitting reservation acknowledgment, the receiving station has acknowledged transmission of the packet data of three packets to the transmitting station B but this transmission station B does not yet transmit the data of the last packet. Therefore, the receiving station sets, for the transmitting station C, the delay information to delay transmission of the packet data as long as the time corresponding to one packet transmission and also sets two packets as the packet number information.
Accordingly, the transmitting station C receives reservation acknowledgment but does not conduct transmission in the next packet data transmission timing and delays transmission for one packet and transmits the packet data in the second next packet data transmission timing.
The transmitting station C transmits the transmitting packet data of two packets in the same manner.
As the prior art for the communication system for reservation, Japanese patent publication document JP-A No. 1997-55693 is listed.
According to the related art explained above, since transmission reservation is conducted in accordance with amount of transmitting data at the transmitting station, the transmitting station can transmit smoothly the transmitting data by utilizing the reserved transmission timing.
However, here rises a problem when amount of data which can be transmitted in each transmission timing changes.
It is not known to allow change in amount of data which can be transmitted in each transmission timing when the transmission is reserved but the items explained below are a part of the items created by the inventors of the present invention.
These items will be explained with reference to FIG. 2.
Since the transmitting station B has the transmitting data of 120 Bytes, upon judgment from the transmission rate in accordance with the present radio environment that data transmission of 40 Bytes in each transmission timing is possible, the transmitting station B judges reservation of three packets is necessary and issues the transmission reservation request of three packets.
However, when the radio environment between the transmitting stations A and B is improve later and the transmission in the higher transmission rate (60 Bytes) is possible, transmission of data is completed with the transmission of two packets without using whole reserved transmission of three packets.
Therefore, the third packet indicated within the frame of dotted line has been reserved but this packet is not actually used as the transmission timing and this packet is no longer useful.
When the radio environment becomes bad, on the contrary, and the transmission rate which is lower than the reserved rate must be used, deviation from the reservation is generated, resulting in competition with the next reservation (refer to competition area in FIG. 3).